1. Field of the Invention
The present invention relates to a network, a private branch exchange, and a multi protocol communication terminal control method for use in the private branch exchange, particularly to a terminal connected to the network including an Internet protocol-private branch exchange (IP-PBX).
2. Related Background Art
This type of network has heretofore been constituted by connection of a private branch exchange to a fixed phone terminal, a radio terminal such as a personal handy-phone system (PHS), a voice over Internet protocol (VoIP) terminal or the like via a local area network (LAN).
As the VoIP terminal, in addition to an IP phone terminal and an Internet phone terminal, there is a session initiation protocol terminal. The SIP is a communication protocol for use in starting or ending multimedia communication such as sound communication (fixed phone, cellular phone, etc.), video communication such as television phone, chat (conversation by characters) and the like in an environment of an IP network using data having a form referred to as an IP packet.
In the IP network, in general, connection-less type communication is performed without confirming connection to a target as in electronic mails. On the other hand, in the fixed phone, in general, connection type communication is performed while confirming the connection with the target. The SIP realizes the connection type communication in the IP network.
The SIP basically comprises methods (operations) such as INVITE (session between users is established), ACK (acknowledgment), CANCEL (INVITE is ended during the establishment of the session), and BYE (the end of the session). The respective methods are exchanged as requests and responses to the requests between clients and servers to thereby establish or end the session.
Moreover, the SIP has characteristics that applications can be comparatively easily prepared. For example, when a new service is added to H.323 of ITU-T for use in the IP phone, an H.450.x protocol which defines the H.323 additional service is added, and all H.323 end points on the network and software of a gate keeper need to be updated. However, in the SIP, an SIP application server which provides the new service is added, and the corresponding application is added. Then, the new service is usable.
However, in the communication between the SIP terminals, there is a problem that only services (e.g., transfer service, service for calling among three, call waiting service, etc.) defined by Internet engineering task force (IETF) can be provided.
That is, even when the SIP terminals are connected to the above-described network in the communication between the SIP terminals, there is a problem that various services (e.g., callback service, extension interruption service, third party control service, etc.) provided by the private branch exchange cannot be received.
Moreover, there is a problem that version of software of the SIP terminal (the above-described client) itself needs to be upgraded to thereby add the service in a case where the new service is added to the communication between the SIP terminals.